feat: implement proxy handler

[abc3]

The current PR introduces a new handler that will replace session mode. It authenticates incoming connections via auth queries, establishes a TCP connection to the tenant's database, and then simply forwards data between the client and the database, functioning primarily as a proxy

• [x] cancel query
• [x] terminate auth_query connection
• [x] active once
• [x] application_name with "via supavisor"
• [x] handle client disconnect
• [x] handle DB disconnect
• [x] auth_query conn is terminated if the client is killed
• [x] telemetry
• [x] delete metrics
• [x] tests

[abc3]

nested or long functions can be simplified before merging v2 into main, once the handler for transaction mode is ready